Fix ReadTheDocs configuration to restore docs updates

- Add .readthedocs.yaml (required by ReadTheDocs for all builds)
- Fix docs/index.rst to include source/modules in toctree
- Add docs/requirements.txt with Sphinx dependencies

Fixes #324

Co-authored-by: Anand Sanmukhani <4n4nd@users.noreply.github.com>

Author: github-actions[bot]

.readthedocs.yaml

@@ -0,0 +1,20 @@
+# ReadTheDocs configuration file
+# See https://docs.readthedocs.io/en/stable/config-file/v2.html for details
+
+version: 2
+
+build:
+  os: ubuntu-22.04
+  tools:
+    python: "3.11"
+
+sphinx:
+  configuration: docs/conf.py
+
+python:
+  install:
+    - requirements: docs/requirements.txt
+    - method: pip
+      path: .
+      extra_requirements:
+        - all

docs/index.rst

@@ -10,6 +10,8 @@ Welcome to Prometheus Client API Python's documentation!
    :maxdepth: 2
    :caption: Contents:
 
+   source/modules
+
 
 
 Indices and tables

docs/requirements.txt

@@ -0,0 +1,2 @@
+sphinx
+sphinx-rtd-theme